A surface emitting device high in luminous efficiency which includes an electroluminescent device such as a light-emitting diode (LED) or organic EL has recently attracted attention. The electroluminescent device is formed from an emissive layer lying between a planar cathode and a planar anode, and generally in many cases, it is formed from a transparent electrode as an anode and a metal reflective electrode as a cathode.
When the cathode is formed from a metal electrode, light is extracted from a side of the transparent anode, and the electroluminescent device is used as a single-emission light emitting device. When electrodes on opposing sides are formed from transparent electrodes, a transparent light emitting device can be obtained and applications to decorative lighting are expected. Light emitted in an emissive layer is not totally extracted. There are a substrate mode in which light is confined in a transparent base material, a waveguide mode in which light is confined in an emissive layer or a transparent electrode, and a plasmon mode in which light is confined in a metal electrode, which are factors for restriction of luminous efficiency of a device.
When an electroluminescent device is used for lighting or as a decorative light source, a color or a luminance of light which comes outside is important. A color or a luminance of light extracted to the outside, however, is varied due to interference with an optical multi-layer, and control thereof is disadvantageously difficult. It is important in applications to estimate a color or a luminance of light extracted to the outside.
A computation method based on a photoluminescence spectrum of a light-emitting material is disclosed in Japanese Laid-Open Patent Publication No. 2010-147337 (PTD 1) and Japanese Laid-Open Patent Publication No. 2009-054382 (PTD 2) as a method of designing a color coordinate or a luminance of light which can be extracted to the outside. A detailed method of computing light extraction efficiency is disclosed in R. Meerheim et. al., Appl. Phys. Lett., 97, 253305 (2010) (NPD 1).